This invention relates to a stator structure of the type used in rotary machines, and more specifically, to structure within the compression section to guide working medium gases through the section.
An axial flow rotary machine, such as a gas turbine engine for an aircraft, has a compression section, a combustion section, and a turbine section. An annular flow path for working medium gases extends axially through the sections of the engine. The gases are compressed in the compression section to raise their temperature and pressure. Fuel is burned with the working medium gases in the combustion section to further increase the temperature of the hot, pressurized gases. The hot, working medium gases are expanded through the turbine section to produce thrust and to extract energy as rotational work from the gases. The rotational work is transferred to the compression section to raise the pressure of the incoming gases.
The compression section and turbine section have a rotor which extends axially through the engine. The rotor is disposed about an axis of rotation Ar. The rotor includes arrays of rotor blades which transfer rotational work between the rotor and the hot working medium gases. Each rotor blade has an airfoil for this purpose which extends outwardly across the working medium flow path. The working medium gases are directed through the airfoils. The airfoils in the turbine section receive energy from the working medium gases and drive the rotor at high speeds about an axis of rotation. The airfoils in the compression section transfer this energy to the working medium gases to compress the gases as the airfoils are driven about the axis of rotation by the rotor.
The engine includes a stator disposed about the rotor. The stator has an outer case and arrays of stator vanes which extend inwardly across the working medium flowpath. The stator extends circumferentially about the working medium flow path to bound the flow path. The stator includes an outer flowpath wall (outer case) and seal elements supported from the wall for this purpose. An example is an inner shroud assembly having a circumferentially extending seal member (rubstrip). The rubstrip is disposed radially about rotating structure and may be supported, for example, by the vanes through an inner shroud. The rubstrip is in close proximity to associated knife-edge seal elements which extend circumferentially on the rotor and together form a seal that blocks the leakage of working medium gases from the flowpath.
The stator vanes and the rotor blades are designed to receive, interact with and discharge the working medium gases as the gases are flowed through the engine. The arrays of stator vanes are disposed upstream of the arrays of rotor blades in both the compression section and turbine section. The stator vanes each have an airfoil located in a predetermined manner with respect to the adjacent stator vanes for guiding the working medium gases to the rotor blades. The airfoils in the forward portion of the compression section are frequently struck by foreign objects that flow into the engine with the incoming stream of gases. These may include large foreign objects such as wild fowl or chunks of ice that may break away from adjacent structure under operative conditions. The stator vane immediately downstream of the fan blade must tolerate these impacts without tearing loose from adjacent structure and moving rearwardly into the adjacent stage of rotating rotor blades. In addition, the stator vanes are frequently replaced over the life of the engine. The replacement vanes are preferably located in a repeatable fashion such that the aerodynamic characteristics of the array of compressor vanes are maintained. Finally, seal elements such as rubstrips formed of silicone rubber which are supported by the stator vanes must tolerate severe rubs from rotating structure. Such rubs may occur during normal operative conditions of the engine or during abnormal operative conditions that might occur, for example, after an impact by a foreign object against the engine. The rubstrip must tolerate the severe rub without delaminating (a noncohesive failure) and moving into the flow path.
The above notwithstanding, scientists and engineers working under the direction of Applicants Assignee have sought to develop stator assemblies having arrays of stator vanes that are locatable in repeatable fashion after replacement and have acceptable levels of durability and replaceability.
According to the present invention, a stator assembly having a plurality of vanes extending through a circumferentially extending casing and into the flowpath for working medium gases has a flat surface at each vane that engages in the installed condition an associated flat surface on a nonflow path surface of the casing.
In accordance with the present invention, the stator vane has a platform having single surfaces on either side of the airfoil which each engage a corresponding flat on the surface of the casing.
In one embodiment, the surfaces are coplanar.
In another embodiment of the present invention, a forged stator vane has a pedestal which is disposed inside the outer case which supports the stator vane and has an opening which receives the airfoil such that the airfoil extends into working medium flowpath. A silicone rubber material may be disposed between the airfoil and the vane to make a flat surface with the flowpath, and with the fillet on the pedestal being buried in the outer case.
A primary feature of the present invention is a stator vane having a flat surface which engages a casing, such as an outer case. Another feature is a casing having a plurality of flats or planar surfaces, each of which is adapted to receive an associated stator vane. Another feature is a stator vane having a pedestal of a size that permits disposing the pedestal entirely within the outer case.
A primary advantage of the present invention is the replaceablility, stability, simplicity of manufacture for a stator assembly and for its stator vanes which results from forming the stator vane with a planar surface that engages a corresponding planar surface on the circumferentially extending outer case. Another advantage is the efficiency of the engine which results from avoiding flow losses associated with vane pedestals that extend into the flowpath.